A method now being widely used, from among several techniques used in fraudulent gambling using a card, such as trump or Korean playing cards (hereinafter referred to as a ‘card’), is a method in which a criminal indicates an invisible substance, such as ultraviolet or infrared ink, on the back of a card and then checks the contents of the card using a special lens, an infrared camera, or an ultraviolet camera, etc.
In general, if an accusation is brought for fraudulent gambling or a gambling scene is arrested, an investigative agency has to often check whether or not a card used is a fraudulent card.
In this case, an appraisal institution is requested to determine whether or not the card is a fraudulent card. In general, appraisers or criminal investigators could know whether or not a mark is present on the back of the card through experiments using a special device on which light of an invisible ray region, such as ultraviolet or infrared, or a bandpass filter of an invisible ray region is mounted.
However, this special device is problematic in that it is expensive and a lot of time is taken to examine whether or not the card is a fraudulent card because a light source having several wavelengths needs to be repeatedly radiated.